good but with "...but..." Rated 2 out of 5 stars
It has potentials and as already mentioned "handy" it can be ...but... creates real mess when adding links in Forums for example. in some forums you may add a link with simple copy/paste and then when previewed and or posted it will be automatically edited as being in [url][/url] brackets. But while you are working in input box writing reply accidental hovering over the link will change it. This causes further misinterpretation when preview/post. There is another bug. It looks like the link amended by QuietUrl upon hovering gets in clipboard or something because found the link getting in different places where current editing of the message take place. Cannot give you more info on the latter bug though due to immediate uninstall of the PluIn cause I needed to get through several Forum posts and all I had to do was brushing up those changed links and removing spare ones before postings
I don't get the problem with the clipboard, because the add-on doesn't use it in any way. It must have something to do with something else. I didn't even really understand what the issue is.
For the writing-post-issue instead, it should really not be so annoying for the simple reason that when you mistakenly hover on a url in a message box (like a text area for a forum message) you have just to click anywhere on the page to un-do the anchor creation which will turn the link back to simple text. Then just keep the mouse out of the text area. Or, you can keep the ctrl key button to hover a link without the anchor being created by the extension. Also, you can completely disable the add-on when writing the post simply by clicking with the right mouse button on the page and going QuietUrl -> Add-on Enabled, un-checking it. If the menu item is checked the add-on is enabled, otherwise it's disabled. Then when you've finished editing the post you can just re-enable the add-on the same way you disabled it, this time checking QuietUrl -> Add-on Enabled. If you want to completely disable the add-on auto anchor creation feature instead you just have to set the preference 'extensions.quieturl.autoUrlTimeout' to 0. Hope this helps.